1. Field of the Invention
This invention relates to a photosensitive material useful in electrophotography which contains a disazo compound as the effective component, particularly, an electrophotographic photosensitive material having a photosensitive layer containing said disazo compound as a material which generates electric charge when irradiated with light (hereinafter referred to as a "charge-generating material").
This invention further relates to a novel disazo compound used for said photosensitive material, a method for preparing said disazo compound, and a novel tetrazonium salt compound used for preparing said disazo compound.
2. Description of the Prior Art
Heretofore, typically known photosensitive materials included inorganic type photosensitive materials that used selenium and its alloy or a dispersion of zinc oxide sensitized by coloring matter in a binder resin, and organic type photosensitive materials that used a charge transfer complex of 2,4,7-trinitro-9-fluorenone (hereinafter referred to as "TNF") and poly-N-vinylcarbazole (hereinafter referred to as "PVK").
However, these conventional photosensitive materials have not only advantages but also various disadvantages. For example, the selenium type photosensitive material widely used at present has such disadvantages as the manufacturing cost is high due to the severity of the manufacturing conditions; it is difficult to work the material into a belt-like product because of lack of flexibility; and it is difficult to handle because the material is sensitive to heat and mechanical shock. The zinc oxide type photosensitive material can be manufactured at low expense by coating cheap zinc oxide on a substrate, but it has such disadvantages as low sensitivity; the smoothness of the surface, hardness, tensile strength, friction resistance and other mechanical properties are inferior; and the durability for repeated use in a plain paper copier is poor. The photosensitive material using the charge transfer complex of TNF and PVK has a low sensitivity and is unsuitable as a photosensitive material for a high speed copier.
Recently, various studies have been carried out to remove disadvantages of these photosensitive materials, and many photosensitive materials, particularly organic type photosensitive materials, have been proposed. Among them, a laminated type photosensitive material prepared by forming a thin film of an organic pigment on an electro-conductive substrate (charge generating layer) and overlaying a charge transfer material-containing layer (charge transfer layer) on said charge generating layer generally has higher sensitivity and more stable chargeability than the conventional organic type photosensitive materials, and it is practically used in part as a photosensitive material for a plain paper copier.
Examples of this kind of known conventional laminated type photosensitive materials include as follows:
(1) photosensitive material using a thin layer formed by vapor depositing perylene derivatives as a charge transfer layer (see U.S. Pat. No. 3,871,882); PA0 (2) photosensitive material using a thin layer formed by coating an organic amine solution of Chloro Dian Blue as a charge generating layer and hydrazone compound as a charge transfer layer (see Japanese Patent Publication No. 55-42380); PA0 (3) photosensitive material using a thin layer formed by coating an organic solvent dispersion of a distyryl benzene type disazo compound as a charge generating layer and a hydrazone compound as a charge transfer layer (see Japanese Patent Laid Open No. 55-84943); and the like. PA0 (1) The above photosensitive materials using perylene derivatives and oxadiazole derivatives has a disadvantage in that the manufacturing cost is very high because the charge generating layer is formed by vapor deposition. PA0 (2) The above photosensitive material using Chloro Dian Blue and hydrazone compound must also use an organic amine (for example, ethylene diamine) as a coating solvent for forming a charge generating layer which is difficult to handle. Furthermore, it has a disadvantage in that the image reproducibility of a reddish original is poor because the photosensitive wavelength range of the visible light zone lies in the range of about 450-660 nm. Therefore, it is necessary to provide a filter to cut red light when used in a copier, thus being disadvantageous to the design of a copier. PA0 (3) The above photosensitive materials using distyryl benzene type disazo compound and hydrazone compound have an advantage in that the charge generating layer can easily be prepared by coating a dispersion of the disazo compound, but it also has a disadvantage in that the image reproducibility of a reddish original is poor in the same manner as in the above photosensitive material (2) since the photosensitive wave length lies in the range of about 450-700 nm.
However, these conventional laminated type photosensitive materials have not only advantages but also various disadvantages as mentioned below.
In addition to these disazo compounds, other examples of known disazo compounds include benzidine type disazo compounds disclosed in Japanese Patent Laid Open Nos. 47-37543 and 52-55643, stilbene type disazo compounds disclosed in Japanese Patent Laid Open No. 52-8832, and the like. However, the conventional layered type photosensitive materials using these disazo compounds also have the same disadvantages as mentioned above, their sensitivity is low and the image reproducibility of a reddish original is poor because the photosensitive wavelength range of the visible light zone lies in the range of about 450-700 nm.